linux: Use installed X11 header files rather than requiring /imports/x11/include

With this patch, it is no longer neccessary to create the
/imports/x11/include/X11 symlink...

Also, remove the include of xfree86.cf from linux.cf, and define our
own DefaultCCOptions.  Setup to use only -ansi, not -pendantic.

cde/config/imake/Makefile.ini

@@ -11,7 +11,7 @@
 BOOTSTRAPCFLAGS = 
 CC = cc
 CDEBUGFLAGS = -O
-INCLUDES = -I../../include -I../../imports/x11/include/X11
+INCLUDES = -I../../include -I/usr/include/X11 -I../../imports/x11/include/X11
 CFLAGS = $(BOOTSTRAPCFLAGS) $(CDEBUGFLAGS) $(INCLUDES)
 SHELL = /bin/sh
 RM = rm -f